Question

An object placed 4 cm in front of a converging lens produces a real image 12 cm from the lens.
(a) What is the magnification of the image?
(b) What is the focal length of the lens?
(c) Draw a ray diagram to show the formation of image. Mark clearly F and 2F in the diagram.

Answer 1

Converging lens is a convex lens.

Distance of the object from the lens (u) =-4
Distance of the image from the lens (v) = 12

(a) Magnification of the lens is given by: 

`m=v/u` 

⇒`m=12/-4=-3` 

Thus , magnifiation produced by the llens 3. 

(b) Lens formula is given by: 

`1/f=1/v-1/u` 

⇒`1/f=1/12-1/-4` 

⇒`1/f=1/12+1/4` 

⇒`1/f=(1+3)/12` 

⇒`f=3`cm       

(c)